sag

1[intransitive]to hang or bend down in the middle, especially because of weight or pressurea sagging roofThe tent began to sag under the weight of the rain.Your skin starts to sag as you get older.Her shoulders sagged in defeat.

2[intransitive]to become weaker or fewerTheir share of the vote sagged badly at the last election.We tried to revive her sagging spirits.